De Minimis Levels

40 CFR 93 § 153 defines de minimis levels, that is, the minimum threshold for which a conformity determination must be performed, for various criteria pollutants in various areas. The information is summarized here:

Pollutant

Area Type

Tons/Year

Ozone (VOC or NOx)

Serious nonattainment

50

Severe nonattainment

25

Extreme nonattainment

10

Other areas outside an ozone transport region

100

Ozone (NOx)

Marginal and moderate nonattainment inside an ozone transport region

100

Maintenance

100

Ozone (VOC)

Marginal and moderate nonattainment inside an ozone transport region

50

Maintenance within an ozone transport region

50

Maintenance outside an ozone transport region

100

Carbon monoxide, SO2 and NO2

All nonattainment & maintenance

100

PM-10

Serious nonattainment

70

Moderate nonattainment and maintenance

100

PM2.5
Direct emissions, SO2, NOx (unless determined not to be a significant precursor), VOC or ammonia (if determined to be significant precursors)